Ligand Exchange Conduction of Lithium Ion in a Pentaglyme-Lithium Bis(trifluoromethylsulfonyl)amide Super-Concentrated Electrolyte

Abstract

Ligand exchange conduction or hopping conduction which means ions move faster than their ligands or solvents, is one of the striking phenomena in electrochemistry. Here, we report a glyme-based electrolyte where ligand exchange conduction takes place. The electrolyte is a concentrated pentaglyme (G5) solution of lithium bis(trifluoromethylsulfonyl)amide (LiTf2N; Tf = SO2CF3) with molar ratio of [G5]/[LiTf2N] = 1/2. Since a diglyme (G2) solution [G2]/[LiTf2N] = 1/1 which has the same molar ratio of ether oxygen to Li+ ([O]/[Li+] = 3) does not show ligand exchange conduction, the glyme chain length may need to be long enough to bridge Li+ ions, by which the momentum exchange of Li+ ions via solvent molecules is allowed.

Uncorrelated Lithium-Ion Hopping in a Dynamic Solvent–Anion Network

“…In traditional liquid electrolytes, solvation shell molecules are in rapid dynamic exchange with free solvent molecules. − This rapid ligand exchange implies that a Li + can diffuse between different locations simply by exchanging its solvating molecules. Such a ligand exchange/hopping mechanism exists in a range of highly concentrated liquid electrolytes. − However, a high salt concentration in these electrolytes introduces intense ion–ion interactions, which generally reduce conductivity. Moreover, the conductivity of “polymer-in-salt” electrolytes, the polymerized version of highly concentrated liquid electrolytes, is still not suitable for commercial applications, even after several decades of research. , …”

Toward New Ion Conductive Liquids via Ionic Liquids

“…Recently, Murase et al found that Li + diffuses fastest in LiTFSA-rich pentaglyme (G5) mixtures. [29] In systems where Li + hopping is suggested, the Li + transference number is important. Hittorf's response and traditional methods of electromotive force, [30] electromotive force and constant current or constant potential polarization, and NMR methods have been compared for representative electrolytes used in lithium-ion secondary batteries.…”

Diglyme-Based “Solvate Ionic Liquid” Gelled in Poly(vinylidine fluoride-co-hexafluoropropylene): A Flexible Electrolyte for High-Performance Magnesium-Ion Batteries

“…28−30 Glymes-based electrolytes have many important features such as high ionic conductivity (∼10 −3 S cm −1 at ambient temperature), wide range of electrochemical stability window (>4 V), less volatility, and the least flammability and toxicity. 31,32 In addition, such electrolytes show chemical stability along with thermal stability over a wider range of temperatures. The glyme-based electrolytes exhibit much better discharge kinetics and has the ability to retain higher capacity when used in batteries as compared to the other carbonate-based electrolytes.…”

“…via the ether oxygen present in different glymes in a ratio of 1:( n + 1). Such coordination occurs in each molecule by donating its electron density through the lone pair of electrons of the oxygen. − Various studies are reported on the mixture of different salts and glymes, referred to as “solvate ionic liquids (SILs)”, employed as electrolytes in different reported rechargeable batteries. − Glymes-based electrolytes have many important features such as high ionic conductivity (∼10 –3 S cm –1 at ambient temperature), wide range of electrochemical stability window (>4 V), less volatility, and the least flammability and toxicity. , In addition, such electrolytes show chemical stability along with thermal stability over a wider range of temperatures. The glyme-based electrolytes exhibit much better discharge kinetics and has the ability to retain higher capacity when used in batteries as compared to the other carbonate-based electrolytes .…”